If out of 10 selected students for an examination, 3 were of 20 years age, 4 of 21 and 3 of 22 years, the average age of the group is

Correct option is B

Solution

We are tasked to find the average age of the group given the ages and their frequencies.

Step-by-Step Solution:

1. Given Data:

- Number of students aged 20 years: 3

- Number of students aged 21 years: 4

- Number of students aged 22 years: 3

2. Total Number of Students:

\text{Total number of students} = 3 + 4 + 3 = 10

3. Sum of Ages:

Sum of ages for each group:

​$$\text{Sum of ages} = (20 \times 3) + (21 \times 4) + (22 \times 3)$$​

Calculate step-by-step:

​$$20 \times 3 = 60, \quad 21 \times 4 = 84, \quad 22 \times 3 = 66$$​

​$$\text{Sum of ages} = 60 + 84 + 66 = 210$$​

4. Average Age:

Average is given by:

​$$\text{Average Age} = \frac{\text{Sum of Ages}}{\text{Total Number of Students}}$$​

Substituting the values:

​$$\text{Average Age} = \frac{210}{10} = 21$$​

Final Answer:

​$$\boxed{21 \, \text{years}}$$​